Thermoplastic tubes that are formed as squeeze tubes are extensively used in packaging of cosmetics, toothpaste, shampoos, and the like. These tubes are formed as tubular members having an open end at a first end and a threaded or other closure-acceptable head at the second end, with a closure used to seal the second end of the tube. The contents of the tube are charged to the tube through the first end. After filling, the first end of the tube is closed, such as by heat sealing, to complete the filled tube for sale.
A problem has existed in formation of such tubes in that the closure-acceptable head is usually formed separately from the tubular member and the provision of a complete seal between the head and tubular member must be assured.
One well known commercial method for producing such headed tubes is that disclosed in U.S. Pat. No. 3,047,910 to M. H. Downs. In this process, a tubular member is placed in a forming collar and a separate molten disc of thermoplastic material is forced into an open end of the tubular member while retained by the forming collar. The latent heat of the molten disc welds the peripheral edge of the disc to the inner circumferential wall of the tubular member and forms an end closure for the tubular member. Pressure is applied to the hot sealed end closure to shape a head into a desired shape and an orifice is then formed through the end of the closure. The head is then fitted with a threaded cap or other closure to provide a closed end tube ready for filling with the desired contents for the tube.
In methods such as that disclosed by the Downs patent, some difficulties remain, such as controlling the thickness and weight of the head and exact color matching of the tubular member and the head. The Downs process is not suitable for commercially preparing tubes from polycarbonates and polyvinyl chloride material. Also, any time two separate units such as a tubular member and a head are combined, a possible source of weakness exists at the juncture of the two. In addition, with such a juncture, a joint between the tubular member and head, a problem of providing a continuous barrier container is present where the tube contains a barrier material, such as an oxygen-barrier containing composite thermoplastic material.
There have been attempts in the past to produce thermoplastic squeeze tubes by extruding a thermoplastic tubing, cutting the tubing into sleeves or tubular members, heating one end of the sleeve to a molten mass and forming it into a head to make the thermoplastic tube. These methods have not been commercially successful because heat transfer is slow and the molten plastic is difficult to control. In such attempts, a sufficient amount of molten thermoplastic material is not accumulated on the end of the tube to form the desired head.
Forming headed thermoplastic tubes from thermoplastic extruded, longitudinally stretched sleeves has worked due in part to the workability of thermoplastic material when it is heated after having been extruded and longitudinally stretched. Such a process is described in U.S. Pat. No. 5,069,856, assigned to the assignee of the present invention and the contents of which are incorporated herein. The process employs the steps of heating a portion of a thermoplastic extruded, longitudinally stretched sleeve by a heat source inserted into an open end of the sleeve to a temperature above the glass transition temperature which causes die swelling (longitudinal shrinking and thickening) of the thermoplastic material and then applying pressure on the heated end of the sleeve by contacting the heated end with a molding die to form a headed thermoplastic tube.